(1) Field of the Invention
The present invention relates to a wet sludge disposal method and facility for efficiently performing final disposal of wet sludge, such as sewage sludge, in a cement clinker manufacturing facility.
(2) Description of Related Art
In disposing of wet sludge, such as sewage sludge, discharged from a sewage disposal plant, the conventional reclamation disposal and ocean disposal have become difficult because of the depletion of disposal sites and the restrictions for preventing environmental pollution in recent years. For this reason, there has been proposed a method for incinerating the wet sludge in an incinerator. However, for example, even the sewage sludge which is formed into a dehydrated cake in the sewage disposal plant contains about 80% moisture.
Therefore, in the disposal method using the incinerator, it is necessary to dry the wet sludge beforehand in order to reduce the thermal load of the incinerator. This results in a problem that the disposal method is inferior in cost effectiveness because additional costs, such as the cost for drying the wet sludge, and the cost for deodorizing exhaust gas generated during the drying treatment are required in addition to the cost originally required for the incineration.
Thus, in order to solve the above described problem, the present applicants have previously proposed, as Japanese Patent No. 3246509 (Patent Document 1) and Japanese Patent No. 3344448 (Patent Document 2), a wet sludge disposal facility and method, in which a cement clinker manufacturing facility is utilized.
Here, the patented invention according to Japanese Patent No. 3246509 is a wet sludge disposal facility, which is installed in combination with a cement clinker manufacturing facility, and which includes a preheater for preheating a cement raw material crushed by a raw-material mill, and a dry process kiln connected to the preheater at the kiln inlet part of the dry process kiln, for calcining the preheated cement raw material. The wet sludge disposal facility is characterized by including: a sludge tank for storing wet sludge; a pressure feed pump for pressure-feeding the wet sludge in the sludge tank; and a pipe connected to the pressure feed pump and configured to directly charge the wet sludge into the dry process kiln, and is characterized in that the pipe is connected to the kiln inlet part or a calcining furnace.
Further, the patented invention according to Japanese Patent No. 3344448 relates to a sludge disposal method characterized in that the wet sludge, while being held in a wet slurry state as it is, is directly charged into the kiln inlet part or the calcining furnace of the dry process kiln which manufactures cement clinker by calcining the cement raw material, by a pump through a pipe, so as to be incinerated.
In the above described wet sludge disposal facility and method, the wet sludge, such as sewage sludge, is directly charged into the existing dry process kiln and incinerated in a high temperature atmosphere of 800° C. to 1200° C., without applying pretreatment such as drying treatment and additive adding treatment, and also without a problem of environmental pollution. Thereby, the final treatment of the wet sludge can be efficiently performed at low cost, and the sludge incineration ash can be economically reused as cement clinker. Further, since the wet sludge is pressure-fed through the pipe so as to be directly incinerated, it is also possible to obtain an effect of preventing a malodor problem and the like.
Meanwhile, for example, when sewage sludge is disposed in the above described disposal method and facility, the sewage sludge whose excess moisture is usually removed is formed into a dehydrated cake having a moisture content of around 80% in the sewage disposal plant mainly for convenience of transportation, and is then transported to the cement manufacturing plant. Here, the dehydrated cake having the moisture content of around 80% has hardness and fluidity equivalent to those of, so to speak, a wet porous clay. For this reason, a pressure feed pump, such as a screw type pump and a piston type pump, capable of obtaining high discharge pressure is used as the pump for pressure-feeding the sewage sludge to the kiln inlet part, or the like, of the dry process kiln.
On the other hand, in general, in the cement manufacturing facility, a plurality of dry process kilns having a diameter of 4 to 6 m and a length of around 80 m are installed in a broad site, and a preheater having a height of several tens of meters is installed in the kiln inlet part of the dry process kiln. For this reason, the pipe from the sludge tank for storing the wet sludge to the kiln inlet part of the dry process kiln needs to have a length of about 150 to 250 m, and further to have a rising part of 10 to 15 m from the ground level to the kiln inlet part.
As a result, in order to finally secure an extrusion pressure enough to charge the sewage sludge into the kiln inlet part, or the like, at the distal end of the pipe, the pressure at the discharge side of the pressure feed pump needs to be increased to about 90 kg/cm2, which results in a problem that the facility cost is increased because the piping system needs to satisfy a very high withstand pressure specification.
Thus, it is conceivable that the viscosity of the sewage sludge is lowered by feeding water to the sludge tank in which the sewage sludge is received, and thereby the fluidization of the sewage sludge is promoted. However, there is a problem that the heat consumption in the dry process kiln is increased as a result of the increase in the moisture content of the sewage sludge, and thereby the fuel cost is increased so as to lower the economic efficiency.
In addition, simply by adding only water to the sludge tank, only the water is accumulated in the bottom part of the sludge tank so as to be fed, as it is, to the pipe from the pressure feed pump. For this reason, there is a disadvantage that the facility costs and pretreatment costs are also increased because a large-scale stirring apparatus for separately mixing the sewage sludge and the water needs to be additionally provided, and further a measure against malodor generated during the mixing treatment is needed.
Patent Document 1: Japanese Patent No. 3246509
Patent Document 2: Japanese Patent No. 3344448